Solar options for home in 2022

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#3495999 27-May-2026 21:03

kangaroo13:

With your very flat pitch: effectively 3 degrees, vs about 30-35 "ideal", your panels are going to be putting out well below their nominal rating over winter - so you'll need to bung up a whole lot more.

agreed, plus if they are less than 20 degrees, then they won’t self clean so easily so you will suffer losses from dirt etc. build up.

kangaroo13:

At the moment we are in a fortunate position of reasonable feed in tarrifs in New Zealand (despite what some in the government say ... look across the ditch where you're lucky to get a few cents, whereas here we can get 17c or more per kWh). But, don't bank on this lasting. I wouldn't build your "business case" on creating credits from summer excess to cover winter costs. Feed in tarrifs are likely to fall once solar uptake increases.

agreed. With falling FIT prices, it gets less attractive to build a system greater than you can use.

https://reneweconomy.com.au/state-says-households-should-get-paid-up-to-33c-kwh-for-rooftop-solar-exported-into-evening-peak/ has written

“IPART says consumers in NSW can expect to receive a flat rate solar feed-in tariff (FiT) between 3.4 to 6.5 c/kWh from their retailer for the solar energy they export to the grid over the course of the day, down from 4.8 to 7.3 c/kWh in 2025-26, when the benchmark FiT got a rare boost.

IPART tribunal member Jonathan Coppel said on Monday that the FiT reduction reflects the regulator’s estimate of the wholesale price of electricity, when solar is exported to the grid, has fallen.

“The decrease is mainly due to increasing electricity generation from grid-wide renewables and rooftop solar increasing the supply of electricity and putting downward pressure on prices,” Coppel said.”

timmmay

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#3496003 27-May-2026 21:39

kangaroo13:

I'd size your array to ensure adequate winter performance. Make sure you can cover your biggest loads on a poor to middling winter's day, and ideally even 'break even' financially on a typical winters day. More than likely this means you'll get a bit of clipping on good summer days, but that shouldn't be a major concern. Panels are the cheap part of the system, so getting good utilisation of your inverter and good self-consumption rates in winter is likely a higher priority.

I'm not sure I'd go with that approach. On a poor winters day, with north facing panels in Wellington, we can get 1-2kwh on a bad day. On a good day, maybe 20kwh, with 9kw of panels.

The way I think of it is power in summer is close to free, the rest of the year we get a varying level of discount off our bill. The main thing for me is the payback period, which is about 6-7 years.

kangaroo13

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#3496004 27-May-2026 22:00

timmmay:

kangaroo13:

I'd size your array to ensure adequate winter performance. Make sure you can cover your biggest loads on a poor to middling winter's day, and ideally even 'break even' financially on a typical winters day. More than likely this means you'll get a bit of clipping on good summer days, but that shouldn't be a major concern. Panels are the cheap part of the system, so getting good utilisation of your inverter and good self-consumption rates in winter is likely a higher priority.

I'm not sure I'd go with that approach. On a poor winters day, with north facing panels in Wellington, we can get 1-2kwh on a bad day. On a good day, maybe 20kwh, with 9kw of panels.

The way I think of it is power in summer is close to free, the rest of the year we get a varying level of discount off our bill. The main thing for me is the payback period, which is about 6-7 years.

Depends what aspect of what I mentioned you're skeptical about.

I agree that winter 'break even' is aspirational.

Nevertheless, I do think it is worth looking at meeting your biggest load on an average-ish winter's day. i.e. if you have a 3kW electric hot water system, then I think it is a good goal to be able to cover that 3kW load on at least a good fraction of winter days. Self consumption is the key to good payback, and hot water is one of the biggest uses of electricity (assuming a conventional immersion element heater).

There are other ways you can achieve this of course, for example a solar diverter (fairly affordable: about equivalent to adding 2 more panels). Or switching to a hot water heat pump - probably not an option for most, unless it's a new build or planning a hot water system replacement anyways (e.g. gas to electricity)

EV charging may change all this up- not a consideration for us as yet. I assume smart/adaptable charging will be key, as sizing solar for rapid charging of an EV is just not realistic.

Agreed that the ultimate measure is payback period. Which for the two systems I've had installed sits around an estimated 7-7.5 years (and we seem to be slightly beating that about 1 year in ...)

Alas -the same analysis suggests that batteries are not yet financially viable for us, with payback well over 10 years, and potentially approaching the projected useful life of the battery.

LightbulbNeil

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#3496008 28-May-2026 00:10

timmmay:

kangaroo13:

I'd size your array to ensure adequate winter performance. Make sure you can cover your biggest loads on a poor to middling winter's day, and ideally even 'break even' financially on a typical winters day. More than likely this means you'll get a bit of clipping on good summer days, but that shouldn't be a major concern. Panels are the cheap part of the system, so getting good utilisation of your inverter and good self-consumption rates in winter is likely a higher priority.

I'm not sure I'd go with that approach. On a poor winters day, with north facing panels in Wellington, we can get 1-2kwh on a bad day. On a good day, maybe 20kwh, with 9kw of panels.

The way I think of it is power in summer is close to free, the rest of the year we get a varying level of discount off our bill. The main thing for me is the payback period, which is about 6-7 years.

We went with a 15 kw system. It will pay for itself by Jan 2029. We installed it back in October of 23 and was making power for 1st of Nov 23. Even though it cost about 30k, the amount it generates in winter and the offset sale to the grid in summer is we have no poaer bill at all. That will change in Nov 2028 when our current contract runs out. Well ahead of the estimated at the time of install of paying back to be 8.5 years. The biggest issue facing all consumers is going to be the line charges in about 5 to 6 years time from now. That is why I am looking at the options to see what is needed to esentially be off grid. Even looking at electric cars etc that will be capable of powering some of the house or transfering the charge to the house battery etc.

In some places , even a 20kw system won't be enough without a huge battery to carry over for 4 to 5 days of power usage. But when line charges get to over 1600 per year, a small generator may actually be a viable option for people to charge a battery .

Energy is changing, and so is more energy effecient appliances etc too. From a well insulated and dry home to a poorly insulated damp home, the energy bill is very substantial that is for sure.

It is a good discussion though and there are many thoughts on it tha's for sure.

timmmay

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#3496025 28-May-2026 07:21

kangaroo13:

Depends what aspect of what I mentioned you're skeptical about.

I agree that winter 'break even' is aspirational.

Sizing for your largest load for a good day in winter is fine, but catering for a bad day in winter would have a hugely oversized set of panels for me. Bad winters days we get almost no solar. Good winters days we do ok, peak generation is about 60 - 70% of summer, but the sun isn't out as long so we don't generate near as much power.

sen8or

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#3496033 28-May-2026 08:36

For me over winter, I define break even as new power bill + interest cost on solar loan, hoping that I can come somewhere close to what I would otherwise have paid if I didn't have solar at all. I can use the data from the inverter to calculate what power I have actually consumed and work out what my bill would have been. If its somewhere close over winter, then over summer we have to be on a win.

Paul1977

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#3496109 28-May-2026 11:54

kangaroo13:

I agree that winter 'break even' is aspirational.

It's that aspiring to an unrealistic goal? Break-even over Winter just doesn't seem realistic if you aren't talking about relying on credits you've earned in Summer. Not unless you have a crazy big array, which (I assume) would also require a crazy big inverter as you can only over provision so much right? Also need pretty sizable battery capacity.

Let's say on a sunny Winter day you can generate 40 kWh from 20 panels, to achieve the same 40 kWh on a terrible Winter day you might need 400 panels.

kangaroo13

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#3496172 28-May-2026 12:55

Paul1977:

kangaroo13:

I agree that winter 'break even' is aspirational.

It's that aspiring to an unrealistic goal? Break-even over Winter just doesn't seem realistic if you aren't talking about relying on credits you've earned in Summer. Not unless you have a crazy big array, which (I assume) would also require a crazy big inverter as you can only over provision so much right? Also need pretty sizable battery capacity.

Let's say on a sunny Winter day you can generate 40 kWh from 20 panels, to achieve the same 40 kWh on a terrible Winter day you might need 400 panels.

I'm absolutely not suggesting you should try to achieve the 'same' 40kWh on a bad winter's day.

Winter break-even on electricity charges (putting aside the standing charge) is not so unrealistic. Even with some pretty dreary days in Christchurch over the last month, my bill for the month-to-date is $34, which includes my standing charge @ $1.38/day ($38), so I'm actually $4 ahead on electricity costs - not bad for May. We'll probably dip slightly into the red over June and July - so, yes, it's a tad aspirational to break even on those months, but we won't be far away.

Here's the logic I've applied:

Size the inverter to cover peak household need over the year.
The cost of the inverter and installation is the expensive part, and the incremental cost of panels is pretty cheap (assuming you have enough suitable roof space).
You get good return when you self-consume, and smaller returns when you sell electricity back to the grid (with this likely to go down over time)
So - put up as many panels as your inverter & roof can take up to the point where you would go beyond the ability to self-consume, even on a reasonable winter's day. i.e. size for your largest load, e.g. hot water system, for a typical winter's day, as on those days you're still getting a good return on your panels as you're able to consume that energy yourself. Oversizing panels to the point where your daily peak in winter is frequently beyond the level you could self-consume pushes you into diminishing returns.

Inverters can take substantially oversized arrays, e.g.

Solis rated at +50%: I've had 6.7KWp into a 5kW Solis,
Sigen rated at +100%: my current system is 9kWp into 6kW Sigenergy, and that can heat my 3kW hot water system even on a fair-to-middling winter's day, noting that the majority of my panels are facing W due to limited N facing roofspace. I've maxed out my N facing roof, and maxed out the number of panels on the W facing string. I'm using a Catch Relay to turn on the HWS when excess solar is sufficient. End result - even as winter approaches I'm getting a good level of self-consumption, and only on quite dreary - such as today - will I need to top up my HWS overnight on off-peak rates (today's peak 2.85kW, which lasted for < 10mins).

Paul1977

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#3496226 28-May-2026 13:57

kangaroo13:

I'm absolutely not suggesting you should try to achieve the 'same' 40kWh on a bad winter's day.

Winter break-even on electricity charges (putting aside the standing charge) is not so unrealistic. Even with some pretty dreary days in Christchurch over the last month, my bill for the month-to-date is $34, which includes my standing charge @ $1.38/day ($38), so I'm actually $4 ahead on electricity costs - not bad for May. We'll probably dip slightly into the red over June and July - so, yes, it's a tad aspirational to break even on those months, but we won't be far away.

Here's the logic I've applied:

Size the inverter to cover peak household need over the year.
The cost of the inverter and installation is the expensive part, and the incremental cost of panels is pretty cheap (assuming you have enough suitable roof space).
You get good return when you self-consume, and smaller returns when you sell electricity back to the grid (with this likely to go down over time)
So - put up as many panels as your inverter & roof can take up to the point where you would go beyond the ability to self-consume, even on a reasonable winter's day. i.e. size for your largest load, e.g. hot water system, for a typical winter's day, as on those days you're still getting a good return on your panels as you're able to consume that energy yourself. Oversizing panels to the point where your daily peak in winter is frequently beyond the level you could self-consume pushes you into diminishing returns.
Inverters can take substantially oversized arrays, e.g.

Solis rated at +50%: I've had 6.7KWp into a 5kW Solis,
Sigen rated at +100%: my current system is 9kWp into 6kW Sigenergy, and that can heat my 3kW hot water system even on a fair-to-middling winter's day, noting that the majority of my panels are facing W due to limited N facing roofspace. I've maxed out my N facing roof, and maxed out the number of panels on the W facing string. I'm using a Catch Relay to turn on the HWS when excess solar is sufficient. End result - even as winter approaches I'm getting a good level of self-consumption, and only on quite dreary - such as today - will I need to top up my HWS overnight on off-peak rates (today's peak 2.85kW, which lasted for < 10mins).

I was looking more as if the objective was being off-grid. So no daily fee, but also no ability to export or import to and from the grid.

Paul1977

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#3496236 28-May-2026 14:44

sen8or:

For me over winter, I define break even as new power bill + interest cost on solar loan, hoping that I can come somewhere close to what I would otherwise have paid if I didn't have solar at all. I can use the data from the inverter to calculate what power I have actually consumed and work out what my bill would have been. If its somewhere close over winter, then over summer we have to be on a win.

Interest cost on loan, or the total monthly repayment amount? Interest on its own would be pretty negligible, wouldn't it?

With Westpac our loan is 0% over 5 years. But the payback period of the system worked out more like 7-8 years (at current power pricing). So we're fully expecting our total outgoing for power (power bill + loan repayments) to be higher than pre-solar for 5 years until the loan is paid off.

sen8or

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#3496242 28-May-2026 15:14

Yeah, I meant total repayment amount (which I think has been structured over about 10 years, but 3 years @ 1%). I do intend setting up a sheet with a depreciation cost for the capital equipment amortised over a set period (8 or so years), then tracking actual vs predicted power bills along with the amortisation cost to see what the real benefit is. I don't know how long I'll run it for, but I've tracked our total debt each month for the last 5 or so years, so I should be able to keep this going for a while.

Paul1977

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#3496257 28-May-2026 16:24

sen8or:

Yeah, I meant total repayment amount (which I think has been structured over about 10 years, but 3 years @ 1%). I do intend setting up a sheet with a depreciation cost for the capital equipment amortised over a set period (8 or so years), then tracking actual vs predicted power bills along with the amortisation cost to see what the real benefit is. I don't know how long I'll run it for, but I've tracked our total debt each month for the last 5 or so years, so I should be able to keep this going for a while.

We aim to fully pay ours off within in the 5 year 0% term. So a little extra belt tightening now, but it shouldn't be too bad.

Stu1

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#3496258 28-May-2026 16:29

Paul1977:

sen8or:

Yeah, I meant total repayment amount (which I think has been structured over about 10 years, but 3 years @ 1%). I do intend setting up a sheet with a depreciation cost for the capital equipment amortised over a set period (8 or so years), then tracking actual vs predicted power bills along with the amortisation cost to see what the real benefit is. I don't know how long I'll run it for, but I've tracked our total debt each month for the last 5 or so years, so I should be able to keep this going for a while.

We aim to fully pay ours off within in the 5 year 0% term. So a little extra belt tightening now, but it shouldn't be too bad.

We have the same loan, without it, I doubt the payback would be worth it or extremely long

Paul1977

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#3496259 28-May-2026 16:38

Stu1:

We have the same loan, without it, I doubt the payback would be worth it or extremely long

It would certainly push the payback period out, but even throwing it on your regular mortgage could still make sense. I think you'd just want to get it paid off before you stop working full time.

fastbike

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#3496262 28-May-2026 16:52

Paul1977:

Stu1:

We have the same loan, without it, I doubt the payback would be worth it or extremely long

It would certainly push the payback period out, but even throwing it on your regular mortgage could still make sense. I think you'd just want to get it paid off before you stop working full time.

Interesting. We self funded it up front as I ended up with many invoices rather than the one the bank demanded for a cheap loan (I did much of the installation myself, getting a sparky and inspector to do the restricted bits). So saved loads of cash up front.

But I'm curious about the fixation with payback and ROI, I spend plenty of other money without demanding that (eating out, holidays, toys etc). I have friends that are always remodelling their homes, replacing perfectly servicable vehicles etc. None of this has a payback / ROI.

My motivations are to get some independence from rising power bills, to avoid importing power when FF production is firming the system, the tech aspects (we are on geekzone after all) and another toy to play with. Plus the boasting factor LoL

Otautahi Christchurch

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